Field of the Invention:
The invention relates to an electrical heating conductor arrangement for heating a furnace, the heating conductor having one or more strip-shaped portions with an essentially horizontal sheet-like extent, which are provided with an arcuate curvature with respect to a horizontal plane H.
EP 1 170 979 B1 describes a corresponding electrical heating conductor arrangement for a furnace for the heating of glass panes. In this arrangement, the heating conductor is produced in plate form, alternate slitting of the plate achieving a plurality of strip-shaped portions having an overall meandering run of the heating conductor. This meander is supported on both sides, over its entire extent, in corresponding recesses of stationary ceramic carrier devices and between these carrier devices has, with respect to a horizontal plane H, an arcuate run curved upwardly.
Materials mentioned for the heating conductor are Fe—Cr—Al alloys and Ni—Cr alloys, by means of which furnace temperatures of at most 1300° C. can be achieved.
In operation, during the heating of the heating conductor, its curvature increases due to the thermally induced expansion of the heating conductor material and due to its rigid clamping between the carrier devices. During cooling, the heating conductor contracts again and returns to its original curvature. This persistent alternating mechanical stress often results in the heating conductor material being overstressed, which may lead to fracture or premature failure of the heating conductor. Particularly when heating conductor materials, such as Mo or W, are used, these being employed to reach maximum furnace temperatures of the order of 1700° C. and above, a heating conductor arrangement of this type results in rapid failure of the heating conductor.